I can't remember a problem exactly like this before, but we have had so many problems with SoundBlaster cards/on-board sound that they all tend to blend in to one big painful mass in my memory. If Steem is running at 100% speed then this is almost certainly caused by sound drivers. If possible try as many versions as you can hold of and hopefully one will work.
If Steem is running below 100% speed then you have a different problem, there are many causes (drivers are the main one again). Contact me if this is your problem and I'll go through the many solutions Steem users have found to fix it.
RE: Sound in STeem